Method of harmonic or subharmonic frequency production



f Patented Feb. 24, 1925.

men STATES PATENT OFFICE.

T Jo'rrNc. sOH LL Nc, or EASTORAIfGE, EW JERSEY, AssIeNoE '10 WESTERN EL G- TRIO COMIANY, NOOEPOEATED, OF NEW YORK, N. a coRro AaION OF NEW YORK.

] mnrnon or. nemiomc OE sonnnnmomc FREQUENCY PRODUCTION.

Application filed December 29, 1923. Serial No. .683,303.

To all whom it may concern:

Be it known that I, JOHN C. SOHELILENG, a citizen, of the -United States of America, residing at East Orange, in; the county of Essex and State of New Jersey, have invented certain new and useful Improvements in Methods of Harmonic or Subharmonic Frequency Production, of which the following is a full, clear,.concise, and exact description. I

' This invention relatesto the production of oscillations and particularly, to methods of and systems forthe production of oscillations the frequency of which has a definite 5 relation to the frequencies ofthe currents from one or more different sources. An object of the invention is to generate ple or sub-multiple of a given frequency.

Another object of the invention is to produce a wave which has a frequency equal to the average of the frequencies of the upper and lower side bands Of a modulated carrier wave, that is, to produce a wave whose frequency is the arithmetic means of the frequencies of the twoside bands.

A still further object is to provide an efii- '(ient circuit for the receptionof a pure modulated wave, including improved means for locally producing and maintaining at the-desired frequency, the unmodulated carricr wave required for signal detection.

The objects of the invention are realized in circuit arrangements utilizing an oscillator for producing a complex wave whose fundamental frequency is normally approximutely that of the desired sub-harmonic frequency and having a harmonic approximately equal to the reference frequency. The current of the reference frequency is causedto coact with the current of the harmonic frequency in the oscillation circuit of the oscillator. The effect of such coaction on the oscillator is to pull it into step with the frequency of the impressed current, that is. to cause the reference and harmonic frequencies to become identical. The fundamental frequency is thus correspondingly automatically adjusted to exact sub-harmonic relationship with the reference frequency.

The above described principle has particular application in a system for deriving a carrier frequency wave from upper and lower side bands based upon the carrier frequency wave and especially in a carrier wave receiving system characterized by the transmission of a pure modulated Wave, that is,

the production at the receiver ,of a wave having at all=times the frequency-of the unmodulated carrier used at the transmitter.

The production of the unmodulated carrier may be accomplished by means of the a wave whose frequency is a desired multipresent invention by combining the received side bands, selecting the resulting compo-- nent of double carrier frequency and cansing it to operate upon a local oscillator in the manner described above to produce the first even sub-harmonic, i. e., the desired carrier frequency. 7

An alternative method involves the step of first producing currents whose frequencies are sub-harmonics of the res ective side band frequencies and then combming these currents to frequency.

It should be noted that the method-of harmonic or sub-harmonic frequency production of the invention is not based on an analysis of the reference wave as 'in com- 'mon forms of harmonic or sub-harmonic producers' It differs essentially also from a typev of harmonic producer illus-' trated for example, by U. S. patent to Affel, No. 1,450,966 issued April 10, 1923, in which produce a current of the carrier a wave having no unmodulated component.

interaction between the reference current and the current derived from a harmonic generator tends to produce a component proportional to the difference in frequency. which, in turn, produces a proportional effect on the frequency of the generator by actuating mechanical impedance varying means, or the like. The method of the invention is marked by simplicity, sensitivity, positiveness of control, direct result, and inherent accuracy.

A better understanding of the invention both in its broad and specific aspects will beafi'ordcd by the following description m which typical embodiments and other objects will be pointed out as the description proceeds.

In the drawing to which reference will now be made, I

Fig. 1 illustrates a sub-harmonic frequency producing arrangement of the lnvent on and also a system in which it may be practically applied and Fig. 2 illustrates another form of arrange ceivetwo side bands of a modulated wave from which the unmodulatedcomponent has been suppressed-and to reproduce therefrom signal modulations. The received waves constituting side bands which are incident on antenna AN are impressed through transformer 1 on modulator M. This modulator may be of'any'type capable of distort-' "ing the impressed waves to 'produce components whose frequencies are the sums and differences of the frequencies of the impressed components. A practical example of vacuum tube modulator adapted for use in the system of Fig. 1 is described in U. S.

patent to Wold, No. 1,424,866, issued Au gust 8, 1922. In this patent the modulator indicated in the drawing by M combines the received side bands in a manner similar to that of the present invention to similarly produce, among other components, a double carrier frequency component.

Filter Fselects the resultant double carrier frequency component to the exclusion of all of the other components. Filters whose design is appropriate to the function here described, are described in Campbell Patent No. 1,227,113. issued May 22. 1917. Amplifier AM amplifies the selected double carrier frequency component and impresses it through transformer 2 on oscillator O. The oscillator illustrated is of the type described in detail in the patent to Hartley, 1.356.763 issued Oct. 26, 1920. Any other type of oscillator may be used provided only that its frequency is determined by the impedance characteristic of a circuit which is adapted to be coupled with external circuits from which control wavesmay be impressed. Oscillator O is designed to generate a wave whose fundamental or a harmonic thereof is approximately the desired frequency and which has a harmonic which has a frequency approximately equal to that im pressed from transformer 2. If the harmonic frequency is sufficiently near the frequency of the impressed current, this cutrent can, under certain conditions, pull the oscillator, through this harmonic, into step with the impressed wave. The fundamental frequency of oscillator 0 together with the other harmonics will undergo '0. corresponding adjustment so as finally to have a frer quency corresponding to anexact sub-har-i monic of the impressed current, the order of this sub-harmonic being determined by the particular harmonic of the fundamental on which the pulling-in effect is exerted;

In the system-illustrated, oscillator O is pulled into step with the double carrier frequency by means of itsfirst even harmonic so that the resultant sub-harmonic has a fre' quency corresponding to that ofthe unmodulated carrier. This carricrfrequency current is transmittedthrough transformer 3 to demodulator DM where it 'is combined with side band currents incident on the antenna and impressed on the modulator from the secondary of transformer 4, to reproduce .the modulated component in indicator 5. Demodulator DM in its essential principle of operation issimilar to a modulator and may utilize a circuit arrangement identical with that used for modulator M.

The theoretical reasons for the function, of the control wave in pulling the oscillator into step with its own frequency is more or less obscure and is incapable of simple mathematical analysis. It is true that this action cannot arise in a system all of whose electrical characteristics are linear. No interaction between fundamental and harmonics, or between any of the two frequencies is possible except through this distorting action of some element of the circuit, such as a space discharge device.

It is old to cause two oscillators to be pulled into step with other oscillators or for one current to pull an oscillator into step with its own frequency. See, for example. U. S. patent to Hazeltine. No. 1,379,184 issued May 24. 1921. Important features of the invention are the utilization of a harmonic ofthe generated wave in performing the function of pulling an oscillator into step and the utilization of one fre uency component for the pulling-in function in order to produce another frequency component of either higher or lower frequency than the first mentioned. and the utilization of the principle of sub-harmonic frequency production 'in producing an unmodulated carrier component from its modulated side bands.

One of the conditions that must be present to insure the success of the pulling-in function is a sutiiciently close initial degree of synchronization. Also, since the effect of the impressed current is similar to that of an actuating means in a system for producing forced ocillations, the couplin should preferably be close. The method o operating the system of Fig. 2 is similarto that of quencies fi 2 and respectively, are produced by the circuits indicated by blocks 8 and 9. These circuits may comprise a combination identical with the combination of amplifier AM, trans- .former 2, oscillator O and transformer 3, of Fig. 1.

i The resultant sub-harmonic frequency I currents are combined in modulator M to yield a component frequency equal to the sum of these frequencies, that is, the unmodulated carrier frequency f. ThlS carrier is utilized in demodulator DM to reproduce the signal component which is indicated in telephones or the like 5 as in Fig. 1, the switch 10 being in its lower os tion.

In the operation of the system' 0 Fig. 2, it is apparently required that the controlled oscillator be kept in step with a variable frequency control current. To the extent that this result is actually realized, that is, that the fundamental frequency has all values of and modulation in modulator M will yield the difference frequency component S, as well as the carrier f. Accordingly, the desired signal may under some conditions be reproduced directly from indicator 11 by actuating switch 10 to its upper position. Obviously a single indicator could be used to perform the functions of indicators 5 and 11.

As a matter of fact, it is impossibleto cause the control oscillator to follow' the multiplicity of frequencies in their complex variations .of amplitude if speech signals, for example are used. In general, however: this failure of the control oscillators to follow rapid variations of the impressed fre quencies is not detrimental to the success of the function of producing the unmodulated earner.

If the frequency of the carrier Wave is so high as to make separation of its-side band '7 by filters F and F, diflicult, the frequency of the incoming side bands may be stepped down by conventional methods. After the sefparation of the corresponding side bands 0 the reduced frequency, they may be stepped up to the original high frequencies. Means for accomplishing this function are common in the art, being described, for example, in U. S. patent to Aifel, No. 1,353,- 698 issued September 21, 1920. -A similar means may be used-in connection with filterv F of Fig. 1 in order to separate the frequency 2 from the component 2 +2S, although it is probable that if both of t iese components were present in the control circuit, the oscillator would tend to keep in step with the constant frequency 2f rather than with the variable frequency.

Although the invention has been described as applied in a radio receiving system, it may equally well be applied in any other system employing modulated carrier waves.

In the claims the word harmonic will be used to define a quantity, which is an integral multiple of another quantity ineluding unity.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations Widely different from those illustrated without departing from the spirit of the invention as defined in the following claims.

lVhat is claimed is:

1. The method which consists in generating a reference frequency wave, generating another wave having a plurality of harmonically related frequency components, the frequency of one of which is approx imately that of the reference frequency, synchronizing one of the harmonic frequencies with the reference frequency by. interaction between the energies corresponding to said frequencies, and utilizing one of the other harmonic frequency components.

2. The method using a source of reference frequency currents and a source of complex currents having harmonically related components and including a frequency determining resonant circuit, which consists in transducing energy from the first source t the frequency determining circuit of the second source to pull the frequency of one of the harmonics of said complex current into step with the frequency of the current from the first source, and utilizing the energy of one of the other harmonics.

3. The method of frequency division, which consists in generating a current having a plurality of harmonics, synchronizing one of the harmonic frequencies with the reference frequency by interaction of the energies corresponding to said frequencies, and utilizing another harmonic which corresponds to the desired fraction of the reference frequency.

4. The method of deriving an unmodulatcd carrier component from its modulated side bands which comprises combining said side bands to produce a double carrier frequency component and producing the first even sub-harmonic of said double frequency component.

5. The method which comprises producing a carrier wave of relativel high frequency and a speech wave, mo ulating the carrier wave by the speech wave to produce side bands and eliminating the unmodulated carrier component, transmitting the side bands to a distant point and there utilizing their energ to control the reproduction of a wave of t 1e carrier frequency.

6. The method which comprises producin a wave of a given frequency from two sid e-bands resulting from the modulation of a wave of said given frequency by a speech wave.

7. The method of deriving an unmodulated carrier component from its modulated side bands, which consists in combinin said side bands, selecting the resultant ouble carrier frequency component, generating a wave having a pronounced first even harmonic, and synchronizing the double carrier frequency component with the said harmonic, whereby the fundamental wave has the frequency of the unmodulated carrier.

8. The method of receiving a modulated wave from which the unmodulated carrier has been suppressed, comprising intermodulating a portion of the side bands of said wave, selecting the resultant double carrier frequency component, generating a wave having a pronounced first even harmonic, synchronizing the frequency of the double carrier frequency wave with said hormonic, and combining the fundamental with another portion of the side bands to reproduce the modulated component.

9. The method of receiving a signal modulated suppressed carrier wave, which comprises independently generating two waves, each of which has a pronounced first even harmonic, synchronizing a portion of each of the side bands of said wave with the even harmonic of one of said generated waves, combining the resultant fundamental component to produce the carrier frequency, and combining said carrier frequency with another portion of each of the side bands to reproduce the signal.

10. The method of frequency division, using an electrical oscillating circuit having a plurality of degrees of freedom, the frequencies of vibration differing from each other at all times by fixed ratios, and a source of reference currents, which consists in using the current of reference frequency to force said circuit into vibration at said,

reference frequency, and utilizing the energy of other modes of vibration.

11. In combination, a source of current, a harmonic oscillator having a resonant frequency determining circuit, means for impressing the current from said source on said circuit to force it into oscillation at a harmonic frequency equal to the frequency of said current, and means for obtaining from said oscillator a current of a different harmonic frequency.

12. A carrier wave system comprising means for producing and transmitting a signal modulated suppressed carrier wave, a receiving conductor therefor, means for combining a portion of the received components of said wave, means for selecting the resultant double carrier frequency component, a harmonic electric discharge oscillator having a resonant frequency determining circuit, means for impressing said double carrier component on said circuit to pull said oscillator into step therewith with reference to the first even harmonic frequency,

means for obtainin the fundamental frequency component rom said oscillator, and means for combining said fundamental frequency component with another portion of the received components to reproduce the signal.

13. The method of obtaining a wave whose frequency is the arithmetic mean of the mean frequencies of two frequency bands each containing at least one frequency, which comprises combining said frequency bands to produce a resultant component whose frequency is the sum of said mean frequencies and producing the first even sub-harmonic of said resultant component.

14:. The method of obtaining a wave whose frequency is the arithmetic mean of the mean frequencies of two frequency bands each containin at least one frequency, which comprises comiining said frequency bands to produce a resultant component whose frequency is the sum of said mean frequencies, generating a current having a plurality of harmonics, synchronizing one of the .harmonic frequencies with the frequency of said resultant component by interaction of the energies corresponding to said frequencies, and utilizing another harmonic which corresponds to the first even sub-harmonic of said result-ant component.

In witness whereof, I hereunto subscribe my name this 26 day of December, A. D.

JOHN C. SCHELLENG. 

